[EDIT]
Say, I have a cell array A consisting of n cells and each of them is a zero vector of size (m,1).
Example: A is a 1x2 cell array A = [100x1 double] [100x1
double]
How can I insert new values to each cells, on the same rows and at the same time without having to write separate lines of code? Can I use cellfun to do so?
For instance, how can I replace the ithrow of the first cell with the new value m and the ithrow of the second cell with the new value n, using a single line of code?
m and n may or may not be the same values.
as in comments noted you may try other options such as array for its efficiency, however as an answer to the question you can use evalin function and using change_cell you can for example change contents of second row fo each cell to the vals just in one line of code!:
A = {[1 2 3],[4 5 6]};
change_cell = #(rownum , vals) evalin(...
'base', ...
[...
'rownum =', int2str(rownum),';',...
'vals=[', num2str(vals),'];',...
'for i = 1:length(A);',...
'A{i}(rownum)=vals(i);',...
'end;'...
]);
change_cell(2, [6 8])
Related
I have a cell array [5x1] which all cells are column vectors such as:
exInt =
[46x1 double]
[54x1 double]
[40x1 double]
[51x1 double]
[ 9x1 double]
I need to have a vector (vec) containing the cells in extInt I need to extract and then I have to convert these into a single column array. Such as:
vec = [1,3];
Output = cell2mat(extInt{vec})
Output should become something an array [86x1 double].
The way I have coded I get:
Error using cell2mat
Too many input arguments.
If possible, I would like to have a solution not using a loop.
The best approach here is to use cat along with a comma-separted list created by {} indexing to yield the expected column vector. We specify the first dimension as the first argument since you have all column vectors and we want the output to also be a column vector.
out = cat(1, extInt{vec})
Given your input, cell2mat attempts to concatenate along the second dimension which will fail for your data since all of the data have different number of rows. This is why (in your example) you had to transpose the data prior to calling cell2mat.
Update
Here is a benchmark to compare execution times between the cat and cell2mat approaches.
function benchit()
nRows = linspace(10, 1000, 100);
[times1, times2] = deal(zeros(size(nRows)));
for k = 1:numel(nRows)
rows = nRows(k);
data = arrayfun(#(x)rand(randi([10, 50], 1), 1), 1:rows, 'uni', 0);
vec = 1:2:numel(data);
times1(k) = timeit(#()cat_method(data, vec));
data = arrayfun(#(x)rand(randi([10, 50], 1), 1), 1:rows, 'uni', 0);
vec = 1:2:numel(data);
times2(k) = timeit(#()cell2mat_method(data, vec));
end
figure
hplot(1) = plot(nRows, times1 * 1000, 'DisplayName', 'cat');
hold on
hplot(2) = plot(nRows, times2 * 1000, 'DisplayName', 'cell2mat');
ylabel('Execution Times (ms)')
xlabel('# of Cell Array Elements')
legend(hplot)
end
function out = cat_method(data, vec)
out = cat(1, data{vec});
end
function out = cell2mat_method(data, vec)
out = cell2mat(data(vec)');
end
The reason for the constant offset between the two is that cell2mat calls cat internally but adds some additional logic on top of it. If you just use cat directly, you circumvent that additional overhead.
You have a small error in your code
Change
Output = cell2mat(extInt{vec});
to
Output = cell2mat(extInt(vec));
For cells, both brackets and parentheses can be used to get information. You can read some more about it here, but to summarize:
Use curly braces {} for setting or getting the contents of cell arrays.
Use parentheses () for indexing into a cell array to collect a subset of cells together in another cell array.
In your example, using brackets with index vector vec will produce 2 separate outputs (I've made a shorter version of extInt below)
extInt = {[1],[2 3],[4 5 6]};
extInt{vec}
ans =
1
ans =
4 5 6
As this is 2 separate outputs, it will also be 2 separate input to the function cell2mat. As this function only takes one input you get an error.
One alternative is in your own solution. Take the two outputs and place them inside a new (unnamed) cell
{extInt{vec}}
ans =
[1] [1x3 double]
Now, this (single) result goes into cell2mat without a problem.
(Note though that you might need to transpose your result before depending on if you have column or row vectors in your cell. The size vector (or matrix) to combine need to match/align.)
Another way as to use parentheses (as above in my solution). Here a subset of the original cell is return. Therefore it goes directly into the cell2matfunction.
extInt(vec)
ans =
[1] [1x3 double]
I have been messing around and I got this working by converting this entry into a new cell array and transposing it so the dimensions remained equivalent for the concatenating process
Output = cell2mat({extInt{vec}}')
use
Output = cell2mat(extInt(vec))
Since you want to address the cells in extInt not the content of the cells
extInt(vec)
extInt{vec}
try those to see whats going on
I wanna ask a question about cell array. Suppose I have a cell array
C={[2 1], [3 5], [15 6]};
I'd like to get all first value of each cell, which are [2, 3 , 15]
however, when I type
C{:}(1);
or
C(:)(1);
There would be some mistakes.
So what is the simplist way to get those numbers.
If every cell is a vector and has the same amount of elements, one way is to create a matrix by stacking all of these cells together and extract out the first column. Use vertcat to help you do that:
CMat = vertcat(C{:});
out = CMat(:,1);
If every cell does not have the same amount of elements, one way is to use cellfun. Use an anonymous function to extract out the first element over each cell array:
out = cellfun(#(x) x(1), C);
The benefit of the above approach is that it doesn't matter if each cell is a vector or matrix. It'll extract the first element for a vector or the top-left corner for a matrix.
I have two column matrices:
size(X) = 50 x 1
size(Y) = 50 x 1
which I got from ind2sub
I want to create a structure str such that
str(i).XYZ returns [X(i), Y(i)] for i in [1,50]
I am trying to use
str = struct('XYZ', num2cell([X,Y]));
However, I believe for this to work properly, I need to modify [X,Y] to a matrix of row vectors, each row vector being [X(i), Y(i)]. Not sure if there is a better approach
You are basically on the right way, but num2cell([X,Y]) creates a 2x50 cell, which results in a 2x50 struct. You want to split your input matrix [X,Y] only among the second dimensions so each cell is a 2x1, use num2cell([X,Y],2)
str = struct('XYZ', num2cell([X,Y],2));
Concatenate the two vectors, convert from matrix to cell, and then from cell to struct array:
str = cell2struct(mat2cell([X Y], ones(1,size(X,1)), size(X,2)+size(Y,2) ).', 'XYZ');
In Matlab, we use textscan to get a cell array from a file or somewhere. But the behavior of the cell array is so strange.
There is the sample code:
>> str = '0.41 8.24 3.57 6.24 9.27';
>> C = textscan(str, '%3.1f %*1d');
>> C
C =
[5x1 double]
We can know that C is a cell array of size 5 * 1. When I use C{1}, C{1}{1} and C(1). I get the following result:
>> C{1}
ans =
0.4000
8.2000
3.5000
6.2000
9.2000
>> C{1}{1}
Cell contents reference from a non-cell array object.
>> C(1)
ans =
[5x1 double]
Why I cannot use C{1}{1} to get the element from the cell array ? Then how can I get the elements from that cell array ?
An example I found on the Internet is :
%% First import the words from the text file into a cell array
fid = fopen(filename);
words = textscan(fid, '%s');
%% Get rid of all the characters that are not letters or numbers
for i=1:numel(words{1,1})
ind = find(isstrprop(words{1,1}{i,1}, 'alphanum') == 0);
words{1,1}{i,1}(ind)=[];
end
As words{1,1}{i,1}(ind)=[] show, what is the mechanism of using {}?
Thanks
Then how can I get the elements from that cell array ?
C = C{:}; % or C = C{1};
Access values by C(1), C(2) and so on
There is a slightly different syntax for indexing into cell arrays and numerical arrays. Your output
>> C
C =
[5x1 double]
is telling you that what you have is a 1x1 cell array, and in that 1 cell is a 5x1 array of doubles. Cell arrays are indexed into with {}, while 'normal' arrays are indexed into with ().
So you want to index into the first element of the cell array, and then index down to the first value in the 5x1 array of doubles using C{1}(1). To get the second value - C{1}(2), and so forth.
If you're familiar with other programming languages, cell arrays are something like arrays of pointers; the operator A(n) is used to get the nth element of the array A, while A{n} gets the object pointed to by the nth element of the array A (or 'contained in the nth cell of cell array A'). If A is not a cell array, A{n} fails.
So, knowing that C is a cell array, here's why you got what you got in the cases you tried -
C{1} returns the 5x1 double array contained in the first cell of C.
C{1}{1} gets the object (call it B) contained in the first cell of C, and then tried to get the object contained in the first cell of B. It fails because B is not a cell array, it is a 5x1 double array.
And C(1) returns the first element of C, which is a single cell containing a 5x1 double array.
But C{1}(1) would get you the first element of the 5x1 array contained in the first cell of C, which is what you are looking for. As #Cheery above me noted, it's probably easier, instead of writing C{1}(1), C{1}(2), ... to remove the 'cell-level' indexing by setting C=C{1}, which means C is now a 5x1 double array, and you can get the elements of it using C(1), C(2), ... Hope that makes sense!
I have a 2D cell array with dynamic row sizes and column sizes. One example:
cell3 = [{'abe' 'basdasd' 'ceee'}; {'d' 'eass' 'feeeeeeeeee'}]
Gives: (with dimension 2 by 3)
'abe' 'basdasd' 'ceee'
'd' 'eass' 'feeeeeeeeee'
I want to be able to combine the columns and reproduce a aggregate string cell array where each string is separated by a single white space. Any idea how to do that?
So the output i am looking for is:
'abe basdasd ceee'
'd eass feeeeeeeeee'
The final dimension is 2 by 1.
Is this possible?
Apply strjoin either in a loop or via cellfun. The latter:
>> cellRows = mat2cell(cell3,ones(size(cell3,1),1),size(cell3,2));
>> out = cellfun(#strjoin,cellRows,'uni',0)
out =
'abe basdasd ceee'
'd eass feeeeeeeeee'
Solution without loops or cellfun:
[m n] = size(cell3);
cellCols = mat2cell(cell3,m,ones(1,n)); %// group by columns
cellColsSpace(1:2:2*size(cell3,2)-1) = cellCols; %// make room (columns)...
cellColsSpace(2:2:2*size(cell3,2)-1) = {{' '}}; %// ...to introduce spaces
%// Note that a cell within cell is needed, because of how strcat works.
result = strcat(cellColsSpace{:});